Conventionally, in a photolithography process for producing a semiconductor device, an image sensing device (CCD or the like), a liquid crystal display device, a thin-film magnetic head or the like, a projection exposure apparatus has been used, such as a stepper or the like for transferring a pattern in a reticle serving as a mask onto each shot area on a wafer (or a glass plate or the like) serving as a substrate, via a projection optical system. With such a projection optical system, it is necessary to position the wafer on an exposure position with high precision. Hence, the wafer is held by a wafer holder by means of vacuum attachment or the like, and conventionally this wafer holder has been fixed on a wafer stage which can be positioned with high precision.
On the contrary, to position a wafer with high precision and at a high speed without being affected by the precision of the mechanical guide face or the like, recently a development of a positioning apparatus for positioning a wafer by lifting a flat table on which the wafer is mounted in a non-contact state has been under way. For example, in U.S. Pat. No. 5,196,745, there is proposed a positioning apparatus in which a permanent magnet with the outside being a N-pole and a permanent magnet with the outside being a S-pole are alternately and two-dimensionally disposed on the upper and lower faces of a table on which a wafer is mounted, and a polyphase coil train corresponding to these permanent magnets is arranged on a fixed body side where the table is housed. With this positioning apparatus, by utilizing the fact that the thrust in the horizontal direction occurs in the polyphase coil where the magnetic flux of the permanent magnets is perpendicular to the table, and the thrust in the vertical direction occurs in the polyphase coil where the magnetic flux is horizontal, the table is positioned in a non-contact state in the directions of six degrees of freedom.
With such a conventional non-contact type positioning apparatus, a plurality of permanent magnets in which the polarity is alternately reversed are attached on the upper and lower faces of the table serving as a movable body. Therefore, the table becomes large, and the weight also becomes heavy. Moreover, the thrust in the vertical direction by means of the polyphase coils is very small, and it has in practice been difficult to lift a table having a large weight only by the vertical thrust.
Moreover, the positioning apparatus requires a coil train having a size twice as large as the moving stroke of the table. Hence there is a problem in that the apparatus becomes large.